android4.4组件分析--service组件-bindService源码分析
6.1.1. bindService
因为有前面分析startService的代码实现过程，则对于bindService的代码分析就不用那么详细介绍，在介绍流程的同时更关注一些细节上的部分。
首先，bindService也是通过 ContextWrapper.bindService，再到ContextImpl的bindService，然后是bindServiceCommon，需要注意的是，传入的ServiceConnection被转换成IServiceConnection类型，
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
UserHandle user) {
IServiceConnection sd;
…
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
mMainThread.getHandler(), flags);
…
int res = ActivityManagerNative.getDefault().bindService(
mMainThread.getApplicationThread(), getActivityToken(),
service, service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, user.getIdentifier());
}
接下去是进入AMS的bindService，再调用ActiveServices.java 的bindServiceLocked，它会把IServiceConnection实例存放到ConnectionRecord里面，并执行bringUpServiceLocked，
int bindServiceLocked(IApplicationThread caller, IBinder token,
Intent service, String resolvedType,
IServiceConnection connection, int flags, int userId) {
…
ConnectionRecord c = new ConnectionRecord(b, activity,
connection, flags, clientLabel, clientIntent);
IBinder binder = connection.asBinder();
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false) != null){
return 0;
}
}
…
if (s.app != null && b.intent.received) {
// Service is already running, so we can immediately
// publish the connection.
try {
c.conn.connected(s.name, b.intent.binder);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + s.shortName
+ " to connection " + c.conn.asBinder()
+ " (in " + c.binding.client.processName + ")", e);
}
// If this is the first app connected back to this binding,
// and the service had previously asked to be told when
// rebound, then do so.
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
}
根据之前的分析ServiceLocked会调用realStartServiceLocked，而realStartServiceLocked则先调用scheduleCreateService，完成service的创建和Oncreate（）的执行，然后执行requestServiceBindingsLocked，这个是bind服务相关处理，最后是sendServiceArgsLocked，这个是Start服务的处理。
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
…
app.thread.scheduleCreateService(r, r.serviceInfo, mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo), app.repProcState);
…
requestServiceBindingsLocked(r, execInFg);
sendServiceArgsLocked(r, execInFg, true);
…
}
requestServiceBindingsLocked再调用ActivityThread的方法scheduleBindService，在ActivityThread.java 中，它发出一个BIND_SERVICE事件，被handleBindService处理，
private void handleBindService(BindServiceData data) {
…
if (!data.rebind) {
IBinder binder = s.onBind(data.intent);
ActivityManagerNative.getDefault().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, 0, 0, 0);
}
…
这里先调用服务的onBind方法，因为服务是重载的，所以会执行具体服务类的方法，并返回服务里的binder实例，这个binder随后会被使用到，
其中AMS的publishService方法被调用，在 ActivityManagerService.java中又会调用 ActiveServices.java 的publishServiceLocked，
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
…
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);
for (int i=0; i<clist.size(); i++) {
ConnectionRecord c = clist.get(i);
…
try {
c.conn.connected(r.name, service);
} …
serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
这里主要调用到c.conn.connected，c就是ConnectionRecord，其成员conn是一个IServiceConnection类型实例，这在前面有提到，connected则是其实现类的方法。
对于IServiceConnection，它是一个接口，位置在(frameworks\base): core/java/android/app/IServiceConnection.aidl，aidl定义如下，它只有一个接口方法connected，
oneway interface IServiceConnection {
void connected(in ComponentName name, IBinder service);
}
其服务端的实现在LoadedApk.java，如下，InnerConnection类是在ServiceDispatcher的内部类，并在ServiceDispatcher的构造函数里面实例化的，其方法connected也是调用的ServiceDispatcher的方法connected，
private static class InnerConnection extendsIServiceConnection.Stub {
final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;
InnerConnection(LoadedApk.ServiceDispatcher sd) {
mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
}
public void connected(ComponentName name, IBinder service) throws RemoteException {
LoadedApk.ServiceDispatcher sd = mDispatcher.get();
if (sd != null) {
sd.connected(name, service);
}
}
}
ServiceDispatcher(ServiceConnection conn,
Context context, Handler activityThread, int flags) {
mIServiceConnection = new InnerConnection(this);
mConnection = conn;
mContext = context;
mActivityThread = activityThread;
mLocation = new ServiceConnectionLeaked(null);
mLocation.fillInStackTrace();
mFlags = flags;
}
这里就再回到我们前面的ContextImpl里面bindServiceCommon方法里面，这里进行ServiceConnection转化为IServiceConnection时，调用了mPackageInfo.getServiceDispatcher，mPackageInfo就是一个LoadedApk实例，
/*package*/ LoadedApk mPackageInfo;
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
UserHandle user) {
IServiceConnection sd;
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
mMainThread.getHandler(), flags);
}
所以，getServiceDispatcher会创建一个ServiceDispatcher实例，并将ServiceDispatcher实例和ServiceConnection实例形成KV对，并在ServiceDispatcher的构造函数里将ServiceConnection实例c赋值给ServiceConnection的成员变量mConnection，
public final IServiceConnection getServiceDispatcher(ServiceConnection c,
Context context, Handler handler, int flags) {
synchronized (mServices) {
LoadedApk.ServiceDispatcher sd = null;
ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(context);
if (map != null) {
sd = map.get(c);
}
if (sd == null) {
sd = new ServiceDispatcher(c, context, handler, flags);
if (map == null) {
map = new ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>();
mServices.put(context, map);
}
map.put(c, sd);
…
}
这样，在执行ServiceDispatcher的connected方法时，就会调用到ServiceConnection的
onServiceConnected，完成绑定ServiceConnection的触发。
public void doConnected(ComponentName name, IBinder service) {
…
if (old != null) {
mConnection.onServiceDisconnected(name);
}
// If there is a new service, it is now connected.
if (service != null) {
mConnection.onServiceConnected(name, service);
}
}
至此，就执行完了bindService的主要过程。
我们下面用一张图来总结这个流程，
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